As the number of different implementations for routing grows, the requirements have become more stringent on routing systems. Contemporary systems have some, but not all, of the desirable properties required for adequate routing. The conventional RSVP-TE specification (RSVP-TE) and GMPLS extensions (GMPLS-RSVP-TE) allow network resources to be explicitly included in a path setup, but not to be explicitly excluded. In some cases it is advantageous to exclude a network resource, such as a highly utilized or congested route, node, link, or system from routes. The consequence of not excluding these resources is that the congested network resource becomes a bottleneck limiting the capability and scalability of the routing system.
In some networks, exclusions can be specified during centralized path computation, and an explicit route which exclude the resources specified is generated as a result. This method is referred to as the Route Server Approach. Other systems, however, rely on the use of loose routes or partially specified abstract nodes. These loose routes are resolved within the network as the hops of the explicit route are evaluated. In these cases exclusions cannot currently be communicated to the nodes that evaluate the routes.
The Route Server Approach suffers from a number of other limitations. It may need to perform many simultaneous path computations across more than one area. This reduces the rapidity of the routing system and causes it to be vulnerable to network loading. For e.g., the route server would need to acquire the link state database of all the areas or Autonomous Systems where the path traverses in order to be able to compute a diverse path.
In light of the foregoing, it can be seen that there exists a need for a mechanism that possesses the ability to setup diverse paths as a result of specifying network resources to exclude as part of a path setup.
The present invention addresses the inability of RSVP-TE and CR-LDP to allow nodes to signal routes or links to exclude in a path setup request. The current RSVP-TE specification (RSVP-TE) and GMPLS extensions (GMPLS-RSVP-TE) allow abstract nodes and resources to be explicitly included in a path setup, using the Explicit Route Object, but not to be explicitly excluded.
Although various prior art routing systems have heretofore been extant for sometime, no such system is known to have all of the advantages and novel features of the system described, and claimed, hereinbelow.